I find myself looking on it as "foolish" rather than "unacceptable". There *are* stalkers and freaks who go after WP editors, and our attitude has generally been that if it's not happening on WP itself, it's not our problem. So I can understand why Essjay thought of the false identity idea as a way to protect himself, and I might well have done it myself when I was his age, not thinking through all the possible ramifications. And he's not violating any WP policy, right?
While that is all absolutely true, it doesn't explain why he chose a fake identity with a PhD and a tenured professorship. I can't see any reason for that other than to get people to respect him more, which is rather disappointing, to say the least. I take anything someone says about themselves under a pseudonym with a pinch of salt, but I still wouldn't expect that kind of deception.